1. Field of the Invention
The present invention pertains to azeotropic and azeotrope-like compositions of 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf) and hydrogen fluoride (HF). More particularly the invention pertains to such azeotropic and azeotrope-like compositions which are useful as intermediates in the production of 2,3,3,3-tetrafluoropropene (HFO-1234yf).
2. Description of the Prior Art
Traditionally, chlorofluorocarbons (CFCs) like trichlorofluoromethane and dichlorodifluoromethane have been used as refrigerants, blowing agents and diluents for gaseous sterilization. In recent years there has been universal concern that completely halogenated chlorofluorocarbons might be detrimental to the Earth's ozone layer. Therefore, stratospherically safer alternatives to these materials are desirable. Consequently, there is a worldwide effort to use fluorine-substituted hydrocarbons which contain fewer or no chlorine substituents. In this regard, 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf), having low ozone depletion potential, is being considered as a replacement for chlorofluorocarbons such as dichlorodifluoromethane in refrigeration systems and trichlorofluoromethane as a blowing agent. The production of HFC's, i.e. compounds containing only carbon, hydrogen and fluorine has been the subject of interest to provide environmentally desirable products for use as solvents, blowing agents, refrigerants, cleaning agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing compositions and power cycle working fluids. It is known in the art to produce fluorocarbons such as HFC's by reacting hydrogen fluoride with various hydrochlorocarbon compounds. Such HFC's are not only considered to be much more environmentally advantageous than hydrochlorofluorocarbons (HCFC's) or chlorofluorocarbons (CFC's) because they are not non-ozone depleting, but also they are non-flammable, and non-toxic as compared to the chlorine containing compounds.
HCFO-1233xf is an intermediate in the production of 2,3,3,3-tetrafluoropropene (HFO-1234yf) which is well known in the art as described in U.S. Applications 20070007488 and 20070197842, the specifications of which are incorporated herein by reference. HFO-1234yf has been disclosed to be an effective refrigerant, heat transfer medium, propellant, foaming agent, blowing agent, gaseous dielectric, sterilant carrier, polymerization medium, particulate removal fluid, carrier fluid, buffing abrasive agent, displacement drying agent and power cycle working fluid.
It has now been found that an important intermediate in the production of substantially pure HFO-1234yf, is an azeotropic or azeotrope-like composition of 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf) and hydrogen fluoride. This intermediate, once formed, may thereafter be separated into its component parts by known extraction techniques. The azeotropic and azeotrope-like compositions find use not only as intermediates in the production of HFO-1234yf, but they are additionally useful as nonaqueous etchant mixtures for etching semiconductors in the electronics industry, as well as compositions for removing surface oxidation from metals. In addition, the formation of an azeotropic or azeotrope-like composition of HCFO-1233xf and hydrogen fluoride is useful in separating a mixture of HCFO-1233xf and an impurity such as a halocarbon, for example, 1,1,1,2,3-pentachloropropane; 1,1,2,3-tetrachloropropene; 2,3,3,3-tetrafluoropropene; 2,3-dichloro-3,3-difluoropropene; 1,1,1,2,2-pentafluoropropane; or 1,2-dichloro-3,3,3-trifluoropropene. When it is desired to separate a mixture of HCFO-1233xf and an impurity, HF is added to form an azeotropic mixture of HCFO-1233xf and hydrogen fluoride, and then the impurity is removed from the azeotropic mixture, such as by distillation or other known means. This binary azeotrope or azeotrope-like composition is then available for separation into its component parts.